The London Stock Exchange PLC’s planned merger with Deutsche Börse AG hit a will after the LSE said it would not sell its online trading platform in Italy as demanded by European antitrust officials. In light of the new developments Sunday, both the LSE and Deutsche Börse, set to create Europe’s largest exchange, saw their shares fall. The collapse follows heightened pressure on the planned financial bridge between continental Europe and Britain post-Brexit​, which will likely isolate the U.K.’s financial center.

LSE: MTS Sale ‘Disproportionate’

The European Commission had made LSE’s sale of a majority stake in MTS, an electronic platform for trading European government bonds and other fixed-income products, a condition for the transaction. In a recent initial response to the ruling, The LSE said it was a “disproportionate” remedy and refused to commit to it.

According to sources close to the matter, both the European Commission and Deutsche Börse were surprised by LSE’s reluctance to sell its stake in MTS, reports Reuters. European antitrust officials intended the sale to bolster the position of LSE’s French rival, the region’s first intra-European exchange, Euronext​.

Mounting Pressure

While the news comes as a shock to some, mounting pressure on the deal after Brexit has forced many to question its viability. After the U.K.’s decision to leave the European Union, many German officials had been calling for the headquarters of the new British-German exchange to be moved to Frankfurt, which the LSE staunchly opposed. Further aggravating the situation was a freshly opened investigation on Deutsche Börse Chief Executive Carsten Kengeter by German state prosecutors over possible insider trading. The executive reportedly denies any wrongdoing.

The future strategies of both exchanges are up in the air, as those disappointed in the outcome wait for a new proposition. Ingo Speich of Union Investment, a shareholder in Deutsche Börse, stated, “I’m certain that they have a plan B ... They will have to put something on the table to keep investors.”

If LSA sticks to its guns and decides to hold onto its stake in the Italian e-trading platform, hopes for the 29 billion euro ($31 billion) bid could be shattered. As of now, it looks like the anticipated combination of the London and Frankfurt bourses​ relies on the Commission changing its ruling, a highly unprecedented and unlikely outcome. (See also: LSE and Deutsche Börse Agree on 'Merger of Equals'.)

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